Springs are vital because they are one of the only permanent arid zone water ways . It’s often assumed that, because they’re in close proximity and are all connected to the same source, springs should be pretty similar to each other and remain stable through time. But, is this true? Do springs provide a spatiotemporally stable environment for the species that rely on them? And, if they don’t do all endemic species respond to environmental variance in the same way?
In this second publication from my thesis, I show that springs provide a heterogeneous environment in both space (i.e. not all springs are the same, not all areas within a spring are the same) and time (i.e. the same spring looks very different in summer than winter). Stability can only be found in the deep pools of large springs and the majority of snail species rely on these stable areas.
If all spring are the same and stay the same through time, and if all species endemic to springs live in all parts of all springs in the same way, the only thing stopping every species from living in every spring is their inability to traverse the dry sections of desert between springs . But what if springs differ from each other, and what if springs species are fussy and only like living under particular types of environmental conditions?
When you spend a lot of time in springs, you realise there’s many different kinds – there’s big deep ones, there’s little shallow ones, there’s springs that are little more than a wet spot on the ground. These springs exist in a region characterised by environmental variance – for example deserts have huge fluctuations in temperature and are generally dry, but in the north, experience seasonal rainfall. You also realise that different animals and plants are more common in particular types, or particular areas of springs (something we hinted at in our previous paper).
If springs are changeable and species are particular about where they live, that means their distributions are not only a product of their inability to get to new springs, but also whether the spring they arrive at suits their requirements. And if species are very particular about where they live, the amount of habitat for them to live in is even more limited than we currently assume.
So what did you find?
1) No spring is the same, no spring stays the same
In the one year I monitored the springs at Edgbaston, the one major thing I observed was that nothing is the same, and very few places stay the same. Springs waxed and waned in size through the seasons, shallow tail areas grew and shrunk at daily and seasonal cycles, and fluctuated in salinity and pH as the sun dried out areas of shallow water. The only stable place was deep spring pools, generally areas near a spring vent where water was >10mm deep. These were the only places that stayed in the same place, had stable temperatures and stable water chemistry.
2) No snail is the same
The six species of snail I monitored at Edgbaston occupied different springs, and had different patterns of abundance within springs. Most species were only found where water was deep (>10mm) and permanent, and where water chemistry was closer-to-neutral (generally conductivity <2000uS and pH <9). But one species went against the grain and was found in higher abundance in the most extreme and transitory parts of springs – the shallow spring tails.
3) Distribution isn’t just about dispersal
These findings help us explain why some species are found in so few springs. If sensitive species like Glyptophysa sp. are restricted to places where water is permanent, deep and stable, then they are restricted to the large deep springs that provide these conditions. Alternatively, tolerant species like Jardinella edgbastonensis can live anywhere, so small springs composed of shallow variable areas only are fine for them.
These findings mean we need to rethink how much habitat is available for these threatened endemic species. For example, for a species like Glyptophysa sp. (on the left in the images below) who is bound to deep permanent pools, there’s very few springs that are big enough to have deep permanent pools – when added together they equate to ~5ha of spring wetland. But even within those, Glyptophysa sp. aren’t occupying the WHOLE spring – they are only found in the deep pools. This means that, using my data, they currently live in only ~0.3ha (3000m2) of that already limited amount of spring wetland.
The findings we present here also emphasise that the match between each species requirements, and where those requirements are satisfied in space and time, means that we can’t assume that something we observe in one spring is the same in another. For example, even though J. edgbastonensis (on the right, in the images above) was the only species found in shallow areas of large and small springs, it was in much higher abundance in small springs where areas of shallow water occurred close to the vent. And even though this species occupied more extreme environments, it was most abundant where salinity was low but water was shallow. This means that, for this species, big springs aren’t necessarily better springs.
4) Arid zone or alpine, it’s all about stability
When visiting Alpine springs in Europe last year, it was pretty obvious how different springs could be, but I also thought a lot about how similar our springs were, even though they were on opposite sides of the world in completely different climatic contexts. Arid areas and alpine areas couldn’t seem more outwardly dissimilar. But they are both characterised by environmental variability – in the arid zone temperatures sky-rocket to >50C on a hot day, and plummet to sub-zero temperatures at night in winter, alpine areas fluctuate from glistening green meadows to frozen tundras with the seasons. But species that live within springs in both of these regions have the potential to live in areas where their life is dictated by this variance (shallow spring tails and outflows), or where they can avoid variance thanks to the stabilising influence of groundwater.
This microhabitat diversity is vital for maintaining diversity in springs, because different species like different things but the highest diversity is going to be found in places where everyone gets what they want. And our results suggest that the majority of species in Australia’s desert springs rely on the environmental stability that only strong groundwater flow into a deep spring pool can provide. This means that compromising those pools (i.e. by letting cattle get stuck in them and die, or by decreasing groundwater pressure) means compromising the stability that fosters diversity and its persistence. It also means sampling in just one place (as we have emphasised before), or at just one time, is not going to tell you the whole story about a spring or about what it is like for endemic species to live there.
- There are lots of papers that emphasise the importance of permanent water for Australia’s arid zone biodiversity. Check out:
Davis, JA, Kerezsy, A, & Nicol, S. (2017). Springs: conserving perennial water is critical in arid landscapes. Biological Conservation.
Box, J. B., Duguid, A., Read, R. E., Kimber, R. G., Knapton, A., Davis, J., & Bowland, A. E. (2008). Central Australian waterbodies: The importance of permanence in a desert landscape. Journal of Arid Environments, 72(8), 1395-1413. doi: 10.1016/j.jaridenv.2008.02.022
- Lots of previous research in springs uses meta-population theory to try to predict which springs will house which species, or how long their populations will persist. In some cases, they assume that springs are the same, or that spring size is the only thing that is important when it comes to environmental conditions. For examples, see:
Tyre, A. J., Possingham, H. P., & Niejalke, D. P. (2001). Detecting environmental impacts on metapopulations of mound spring invertebrates – Assessing an incidence function model. Environment International, 27(2-3), 225-229. doi: 10.1016/s0160-4120(01)00091-5
Nicol, Sam, Haynes, Trevor B., Fensham, Rod J, & Kerezsy, Adam. (2015). Quantifying the impact of Gambusia holbrooki on the extinction risk of the critically endangered red-finned blue-eye. Ecosphere, 6(3), 1-18. doi: 10.1890/ES14-00412.1
This concept is not new, and the amazing review of springs by Marco Cantonati and colleagues was part of the reason I wanted to visit this research group. Cantonati, M., Fureder, L., Gerecke, R., Juttner, I., & Cox, E. J. (2012). Crenic habitats, hotspots for freshwater biodiversity conservation: toward an understanding of their ecology. Freshwater Science, 31(2), 463-480. doi: 10.1899/11-111.1